1. Field of the Invention
The present general inventive concept relates to a cell joining method and network using a proxy coordinator, and more particularly, to a method of joining a cell by using a proxy coordinator in which a device positioned out of a beacon frame reachable area can join the cell without colliding with a device already existing in the cell, and a network therefor.
2. Description of the Related Art
A home network connects information appliances at home, thereby enabling communication between persons, between persons and devices, and between devices. Accordingly, the home network technology allows users to easily control appliances at home without restrictions of space and devices, and provides a wider variety of information items and services.
Recently, consumer appliances, such as TVs, refrigerators, and computers, have been evolving as information appliances through data exchange among appliances. In addition, home appliances using power line communication (PLC) have been introduced so that networked indoor home appliances, lights, and gas valves can be remotely controlled by a mobile phone or through the Internet from an outdoor place.
The PLC means a technology enabling communication through power lines connected to households not using dedicated communication lines.
Also, since the PLC enables communication by loading hundreds of kilohertz to tens of megahertz high frequency signals on the power lines, and at present, power lines are connected to all households, if the power lines are used, the PLC can be easily implemented without requiring separate wiring. That is, only a plug is connected to a power outlet, communication is enabled.
Also, the PLC has been originally developed for controlling consumer electronic appliances on the basis of low speed communication, but with the recent development of high speed power line communication technologies, high speed Internet services can be provided through the PLC even without using the conventional communication networks, and power, flux, and gas can also be automatically checked. In addition, home networks, information appliances, and power line networks can be managed through the PLC and in particular, high speed access technologies using the PLC and a low speed control technology through a home network have been highlighted as next-generation communication technologies.
Meanwhile, MAC technology, which has been suggested by Homeplug Alliance (an alliance of North American power line communication industries), uses a central arbiter method which controls access of transmission media in a time division multiple access (TDMA) method using a coordinator apparatus to transmit and receive a beacon frame. In the MAC technology, an area where PLC communication is possible is defined as a logical cell, which is managed by a beacon frame transmitted by a coordinator, and a device transmits a cell join request to the coordinator in order to join the cell. A device which has successfully joined the cell requests time allocation to the coordinator and by using an allocated time period performs PLC communication. The transmission media include a PLC part as a transmission path between devices, and also include, for example, paired cables, coaxial cables, radio wave links, waveguides, and optical cables.
FIG. 1 is a diagram illustrating a conventional PLC cell 10 and a proxy coordinator relaying a beacon frame.
The PLC cell 10 that is a PLC network is formed by a coordinator 20 and a device (hereinafter referred to as a “first device”) which wants to join the cell 10 transmits a cell join request to the coordinator 20. If the coordinator 20 approves the joining and the first device joins the cell, the first device receives time allocation information on a time which the first device will use, through a beacon frame transmitted from the coordinator 20.
Here, a proxy coordinator 30 can be operated in order to allow the first device positioned out of the beacon frame reachable area to join the cell 10. The proxy coordinator 30 is responsible for relaying the beacon frame.
In order for the first device to access transmission media without colliding with existing devices, the first device should be allocated a time period for its own use and use the time period. Accordingly, the first device transmits a frame including a request (hereinafter a “cell join request”) for the first device to join the cell 10, to the coordinator 20. However, it is difficult to determine when the frame including the cell join request should be transmitted to the coordinator 20 without collision with existing cell devices. That is, since the first device cannot know previously generated time allocation information of the cell 10, the frame transmitted to the cell 10 can interfere with the existing cell 10.
In addition, even though the first device receives the time allocation information of the existing cell 10 through the beacon frame relayed by the proxy coordinator 30, the time when the first device receives the beacon frame is inevitably a predetermined time after the coordinator 20 transmits the beacon frame. Accordingly, the first device receives the relayed beacon frame at a time after the transmission of the beacon frame by the coordinator 20, the time being the sum of a transmission time from the coordinator 20 to the proxy coordinator 30, a processing time in which the proxy coordinator 30 receives and processes the beacon frame, and a transmission time from the proxy coordinator 30 to the first device.
Accordingly, it is difficult to synchronize with the existing cell 10 and communicate with the cell 10. Though a cell join request may be transmitted through a trial and error method using a carrier sense multiple access/collision avoidance (CSMA/CA) method, a collision can result with an existing device which wants to be allocated as a transmission medium from the coordinator 20 and to use the transmission medium.
Accordingly, there is a need to allow a device positioned out of the beacon frame reachable area, to join a cell without colliding with an existing cell device.